Cost of parasite exposure depends on host ontogeny

Fear comes at a cost, and exposure to parasites can elicit non-consumptive effects (NCEs in hosts that come at such a cost. While NCEs are well documented, the influence of host developmental stage on these effects remains poorly understood. Using Drosophila nigrospiracula and its ectoparasite Macrocheles subbadius, we tested whether early-life exposure (egg and pupal stages) to mites altered host development and survival. First, we exposed eggs to direct and indirect mite cues to assess effects on larval emergence. We then conducted two follow-up experiments to evaluate microbial transfer from mites and feeding behaviour. Next, we exposed pupae at two distinct developmental stages and recorded both emergence success and mite longevity. Mites were highly effective at consuming fly eggs, but pupae were resistant to direct parasitism. No NCEs were observed from indirect egg exposure; however, host developmental state significantly influences pupal NCEs. Less developed pupae had reduced emergence when exposed to mites, compared to more developed pupae that had detached from the puparium wall. These results indicate that the cost of parasite exposure is developmentally dependent, and that metamorphosis plays a critical role in shaping host susceptibility to non-consumptive parasite effects.